This invention is related in various aspects to the Extruder of my U.S. Pat. No. 3,305,893 which disclosed a slow-speed screw in an unheated bore force-feeding plastic pellets forward under high pressure into and through a heat-transfer zone for melting and thence to an extrusion die. Melt pressure in that extruder resulted entirely from the mechanical force-feeding action of the screw, with no component of viscous shear build-up pressure. In the present invention, a primary distinguishing feature is the use of a directly motor-driven high-speed screw of relatively small diameter. Other distinguishing features should become apparent from the following detailed disclosure.
Conventional screw extruders in present wide usage employ motors, gear reducers, screws, and thrust bearings which are relatively large, costly in first and maintenance costs, and often lacking in efficiency. Also, in many cases excessive shear working in such extruders results in hot spots and molecular breakdown in the melt. Usually most of the melting heat enters as mechanical shaft power through the screw, and in many cases where intensive mixing is desired, excess shaft power must actually be dissipated as wasted heat energy by auxilliary cooling means. Furthermore, conventional extruders can be somewhat difficult to control because output is sensitive simultaeously to both melt temperature and back pressure. Also, screw changes must often be made to accomodate materials with different characteristics. Related to this is the need to employ complicated screw design theories based on non-Newtonian flow, melt counter-flow in the screw, residence time, and the like.